By geological material is meant artificial or natural materials, such as concrete or rock.
The assessment of the condition of concrete shaft and tunnel linings in underground excavations is difficult since most of the deterioration processes take place in the rock-side or blind-side (in the rock/concrete interface of the lining). Ground water and variations in stress conditions are the main causes and can result in deterioration and damage to the linings. The traditional method of evaluating linings is to extract core samples from the structure and measure the thickness, locate delaminations and test for strength and elastic properties. However, coring is costly and can cause further damage. It would therefore, be advantageous to be able to use non-destructive methods of evaluation.
While seismic systems are known for evaluating underground rock formations by reflective elastic waves, such systems, with their associated apparatus, are quite large, and are not usable in confined spaces.